-
This invention relates to a free fall sensor detecting a
fall state.
-
A free fall sensor has conventionally been incorporated
in appliances such as portable computers to detect a fall state,
thereby protecting hard disks built in the appliances against
damage caused by shock due to the falling. Measures are taken
on the basis of a detection signal generated by the free fall
sensor. For example, a magnetic head of the hard disk is moved
to an evacuation position.
-
The free fall sensors are required to be miniaturized in
order to be built into appliances. JP-A-2000-195206
(hereinafter, "document 1") discloses one example of the
foregoing free fall sensors. The free fall sensor disclosed in
document 1 comprises a cylindrical electrically conductive
container serving as a fixed electrode, a flexible beam or
bar-like spring horizontally cantilevered in the container and
connected to one of two ends of an electrically conductive pin
with the other end facing an exterior, and a steel ball provided
as a weight at a free end side of the spring. The steel ball
functions as a movable electrode which is brought into contact
with and departed from the container.
-
In a normal stationary state of the free fall sensor of
document 1, the spring is subjected to the gravity of the steel
ball thereby to be flexed, whereby the steel ball is brought into
contact with an inner face of the container such that an
electrical path is formed. On the other hand, apparent
gravitational acceleration acting on the steel ball is reduced
during fall such that the steel ball is in zero gravity. As a
result, the spring returns to the horizontal free state by its
resilience, whereupon the steel ball parts from the inner face
of the container, breaking the electrical path. Thus, the
aforementioned free fall sensor is capable of detecting the fall
state on the basis of break of the electrical path.
-
JP-A-2001-185012 (hereinafter, "document 2") discloses
another free fall sensor. The free fall sensor disclosed in
document 2 employs a compression coil spring as the spring and
has substantially the same function as the above-described free
fall sensor of document 1. In particular, a cylindrical weight
is provided around the compression coil spring, so that the length
of the sensor can further be reduced, whereupon the sensor can
further be miniaturized.
-
However, a single bar-like spring is employed as the spring
in the free fall sensor of document 1. In a case where the weight
flexes the cantilevered free end when the sensor has suffered
shock due to fall, bending stress is concentrated on the bar-like
spring such that the spring is liable to be plastically deformed
partially or buckled. Accordingly, the spring serving as the
movable electrode cannot be retained at a normal position thereof
for a long time of use, thereby resulting in an instable switching
operation. Consequently, the sensor of document 1 has problems
in the durability of the spring. Moreover, when the weight of
the steel ball or the spring force of the spring is reduced for
the purpose of further miniaturization of the free fall sensor,
other factors of instability such as poor contact are added since
a contact pressure is reduced between the steel ball and the
conductive container. In consideration of the flexibility and
durability of the spring and spherical weight, it is difficult
to design and manufacture a free fall sensor which is well
balanced in these respects. Thus, the free fall sensor of
document 1 is unsuitable for further miniaturization and
particularly for reduction in the thickness which has recently
been desired keenly.
-
On the other hand, the compression coil spring used in the
construction of document 2 can reduce the spring force and act
effectively to return to the free state reliably in the occurrence
of fall. Consequently, the freedom in the design of coil spring
and weight can be increased. Moreover, since the coil spring
has sufficient elasticity, it is effective in preventing partial
buckling thereof as in the aforementioned bar-like spring.
Further, even when the length of the compression coil spring is
rendered smaller as compared with that of the bar-like spring,
a sufficient amount of flexure can be achieved.
-
The construction that the cylindrical weight is provided
around the coil spring is effective for reduction in the length
thereof. However, this construction has a definite limitation
in reduction in the thickness or height. For example, the
overall thickness (or diameter) of the free fall sensor has a
limit of about 5 mm. Additionally, it is never easy to produce
a small-sized weight with high decision by gold-plating the
weight in order that a unique shape of weight may serve as an
electrode. Further, the assembly of the free fall sensor is
complicated. Furthermore, the coil spring is superior to the
bar-like spring since it is hard to suffer the plastic deformation
due to buckling. However, the weight is applied as shock to the
coil spring during fall, and moreover, the direction of shock
is biased. Accordingly, there is a possibility that part of the
coil spring may suffer plastic deformation, which results in an
instable operation of the coil spring or which is a problem in
the durability.
-
Furthermore, the weight forcibly collides against the
conductive container when each of the above-described free fall
sensors suffers shock due to fall, whereupon an abnormal sound
is produced. Additionally, a point of contact is concentrated
on a single point. Consequently, there is a possibility that
soil may be interposed between the electrodes or a long time
service of the sensor may result in formation of an oxide film
between the electrodes. In this case, a stable electrical path
cannot be formed. In particular, when the size of the free fall
sensor is further reduced, the spring force tends to be reduced
and the contact pressure also tends to be reduced. Thus, each
above-described free fall sensor has a problem of further
disadvantage in the practical use.
-
Therefore, an object of the present invention is to provide
a free fall sensor which can restrain bucking and plastic
deformation of the coil spring during fall while realizing
miniaturization and which can expect a stable operation of the
movable electrode for a long period of time.
-
The present invention provides a free fall sensor which
includes an electrically conductive container, an electrically
conductive pin having an end inserted into the container and a
movable electrode provided in the container, characterized in
that the movable electrode includes a coil spring cantilevered
on the end of the conductive pin and a weight provided in an inner
space of the coil spring so as to be movable and so as to be
prevented from falling off.
-
The weight is movably provided in the inner space of the
coil spring in the above-described construction. Accordingly,
the weight effective functions as the movable electrode without
obstructing the flexure of the coil spring. Furthermore, the
weight serves as a core for the coil spring thereby to prevent
the coil spring from such a large deformation that results in
buckling or plastic deformation during fall. Moreover, since
the weight is disposed in the inner space of the coil spring,
no portions radially protrude from the coil spring and the
thickness of the electrode is reduced. Accordingly, the
above-described construction is advantageous when a free fall
sensor is rendered thinner and smaller in the size. Further,
a middle of the coil spring vibrates up and down, thereby
producing a damping effect. The damping effect can damp a sudden
collision against the container, thus improving the durability
of the weight and reducing sound due to collision. Still further,
the electrodes are brought into contact with and parted from each
other repeatedly. In this case, since minute vibration is
absorbed, chattering of the switching function can be reduced.
Additionally, every time the free end of the coil spring is
brought into contact with the container, the coil spring is
expanded and contracted in the lengthwise direction such that
a contact face of each one of the coil spring and the container
slides on the other. Consequently, soil and an oxide film on
the contact faces can be wiped off and accordingly, a stable
switching operation can be achieved for a long time even though
the miniaturization of the free fall sensor tends to reduce the
contact pressure between the electrodes.
-
The invention also provides a free fall sensor which
includes an electrically conductive container, an electrically
conductive pin having an end inserted into the container, and
a movable electrode provided in the container, characterized in
that the movable electrode includes a coil spring fixed to the
end of the conductive pin and having a free end and a weight
provided on the free end of the coil spring, the weight extending
lengthwise from the free end of the coil spring, having a larger
length than a diameter thereof and formed into an oblong
cylindrical shape.
-
The weight is oblong in the above-described free fall
sensor. Accordingly, a required mass can be ensured even though
the diameter of the weight is reduced. Moreover, the weight is
fixed to the coil spring so as to extend in the direction of
elongation of the coil spring. This electrode structure allows
the thickness of the weight to be set at minimum, thereby
rendering the free fall sensor further thinner. Further, the
distal end of the weight away from the center of gravity thereof
is brought into contact with the container and the opposite end
of the weight is connected to the coil spring. Consequently,
a sudden contact or collision with the container can be reduced,
whereupon the sound due to collision can be reduced. Still
further, since minute vibration is absorbed, chattering of the
switching function due to repeated contact and parting between
the electrodes can be reduced. Still further, every time the
weight is brought into contact with the container, the coil spring
is expanded and contracted in the lengthwise direction such that
the weight slides right and left. Consequently, soil and an
oxide film on the contact faces can be wiped off and accordingly,
a stable switching operation can be achieved for a long time even
though the miniaturization of the free fall sensor tends to reduce
the contact pressure between the electrodes. Yet further, the
buckling can be prevented by the employment of the coil spring.
Since the weight is columnar, the free fall sensor can be
assembled without limitation in directivity of the mounting
positions of the weight and the coil spring. Thus, the free fall
sensor can be designed and manufactured easily.
-
The invention further provides a free fall sensor which
includes an electrically conductive container, an electrically
conductive pin having an end inserted into the container, and
a movable electrode provided in the container, characterized in
that the movable electrode includes a coil spring fixed to the
end of the conductive pin and having a free end and a weight
provided on the free end of the coil spring, the coil spring being
provided with a displacement limiter for limiting an amount of
displacement of the coil spring in a direction of compression
to a predetermined range.
-
The free fall sensor can restrain a large displacement in
the direction of compression in subjection to shock due to fall,
which displacement results in partial deformation of the coil
spring. Consequently, plastic deformation caused with large
flexure can be prevented and the coil spring can be protected
from the shock. Accordingly, the free fall sensor can achieve
a stable switching operation for a long time of period, is
superior in the durability and can achieve further
miniaturization.
-
The invention will be described, merely by way of example,
with reference to the accompanying drawings, in which:
- FIG. 1 is a sectional view of the overall construction of
the free fall sensor in accordance with a first embodiment of
the present invention;
- FIG. 2 is a view similar to FIG. 1, showing the free fall
sensor under different condition;
- FIG. 3 is a section taken along line 3-3 in FIG. 2;
- FIGS. 4A to 4C are schematic views explaining the operation
of the free fall sensor in different modes;
- FIGS. 5A to 5D are views of the free fall sensor in the
states before and after assembly;
- FIG. 6 is a view similar to FIG. 1, showing the free fall
sensor of a second embodiment in accordance with the invention;
- FIG. 7 is a view similar to FIG. 2;
- FIG. 8 is a sectional view taken along line 8-8 in FIG.
7;
- FIG. 9 is a view similar to FIG. 1, showing the free fall
sensor of a third embodiment in accordance with the invention;
- FIG. 10 is a view similar to FIG. 1, showing the free fall
sensor of a fourth embodiment in accordance with the invention;
- FIG. 11 is a view similar to FIG. 1, showing the free fall
sensor of a fifth embodiment in accordance with the invention;
- FIG. 12 is a sectional view of the free fall sensor of a
sixth embodiment in accordance with the invention;
- FIG. 13 is a view similar to FIG. 12, showing the free fall
sensor in another state;
- FIGS. 14A to 14C are schematic views of the free fall sensor
in different states;
- FIGS. 15A to 15D are views of the free fall sensor in the
states before and after assembly;
- FIGS. 16A and 16B are views of the free fall sensor of a
seventh embodiment in accordance with the invention, showing the
sensor in an assembling step;
- FIGS. 16C and 16D are views of the free fall sensor of an
eighth embodiment in accordance with the invention, showing the
sensor in an assembling step;
- FIG. 17 is a partially broken sectional view of the free
fall sensor of a ninth embodiment in accordance with the
invention;
- FIG. 18 is a view similar to FIG. 17, showing the free fall
sensor in an operating mode;
- FIG. 19 is a view similar to FIG. 17, showing the free fall
sensor of a tenth embodiment in accordance with the invention;
- FIG. 20 is a view similar to FIG. 17, showing the free fall
sensor of an eleventh embodiment in accordance with the
invention;
- FIG. 21 is a view similar to FIG. 17, showing the free fall
sensor of a twelfth embodiment in accordance with the invention;
- FIG. 22 is a view similar to FIG. 17, showing the free fall
sensor of a thirteenth embodiment in accordance with the
invention; and
- FIG. 23 is a view similar to FIG. 17, showing the free fall
sensor of a fourteenth embodiment in accordance with the
invention.
-
-
A first embodiment of the present invention will be
described with reference to FIGS. 1 to 5D. The free fall sensor
1 in accordance with the first embodiment is provided, for example,
in a portable computer (not shown) such as a notebook-sized
personal computer in an oblong state as shown in FIG. 1. The
free fall sensor 1 comprises a slender cylindrical container 2
having an opening at one end, a closing member 3 for closing the
opening of the container for electrical insulation and
airtightness, an electrically conductive pin 4 extending in an
airtight manner through the closing member 3 into the container
2, and a movable electrode 5 fixed to an end of the conductive
pin 4 inside the container.
-
The container 2 is made of an electrically conductive metal
and formed into the slender cylindrical shape with the one open
end (the left end as viewed in FIG. 1) . The conductive container
2 serves as a fixed electrode as will be described later.
-
The closing member 3 comprises a cylindrical frame 6 and
an electrically conductive filler 7, such as glass, filling the
interior of the frame. The conductive pin 4 extends horizontally
through a centrally located through hole 3a formed in the bottom
of the closing member 3. The frame 6 is force-fitted into the
container 2 thereby to be fixed to the latter. Before the
force-fitting, an inner peripheral surface of the container 2
and an outer peripheral surface of the frame 6 are electroplated
with nickel and gold or gold alloy. Electroplated layers of the
container 2 and frame 6 are integrated together as the result
of force-fitting, whereupon the airtightness is improved. The
frame 6 and container 2 may be welded by laser welding, instead.
-
The container 2 is airtightly closed and the conductive
pin 4 is electrically insulated from the container 2. With this,
the interior of the container 2 is evacuated or filled with an
antioxidant gas such as gaseous nitrogen or gaseous helium in
order that the inner peripheral surface of the container 2 serving
as the fixed electrode may be prevented from oxidation for a long
period of time.
-
The movable electrode 5 is disposed in the container 2
closed as described above. The movable electrode 5 is
electrically brought into contact with and parted from the
container 2 in subjection to fall, shock or the like. An
electrically conductive disc-shaped spring seat 8 and an oblong
compression coil spring 9 are coupled in turn to the end of the
conductive pin 4 inside the container 2. A sphere 10 serving
as a weight is provided in an inner space of the coil spring 9.
The coil spring 9 is made of an electrically conductive metal
such as phosphor bronze or stainless steel and formed into a
cylindrical shape. The coil spring 9 is cantilevered on the
spring seat 8a. When the weight of the sphere 10 is applied to
a free end of the coil spring 9, the coil spring is flexed thereby
to be brought into contact with the container 2. The coil spring
9 normally remains conductive as shown in FIG. 1.
-
The sphere 10 comprises a plurality of steel balls, for
example, five steel balls in the embodiment. The steel balls
are provided in the inner space of the coil spring 9 so as to
be movable. More specifically, as shown in FIG. 2, the sphere
10 has a diameter D1 set so as to be smaller than an inner diameter
D2 of the coil spring 9 (D1<D2) . Five aligned steel balls have
a total length L1 set so as to be smaller than substantially the
effective free length L2 of the coil spring 9 (L1<L2) . The sphere
10 is provided in the inner space of the coil spring 9 so as to
be movable freely and serves as a core protecting the coil spring
as will be described later. Accordingly, the above-described
free length L2 of the coil spring 9 is within a range of distance
that the sphere 10 is moved.- The diameter D1 of the sphere 10
is set to be not less than one half of the inner diameter D2 of
the coil spring 9 (D1≥D2/2). Consequently, the steel balls
constituting the sphere 10 are aligned so as to be prevented from
being vertically laid one upon another and so as to be normally
adjacent to one another transversely, whereupon the steel balls
can be moved smoothly.
-
The coil spring 9 has a proximal end 9a is fixed to the
above-described cylindrical portion 8a of the spring seat 8 by
an electrically conductive adhesive agent, whereby the coil
spring 9 is cantilevered. The spring seat 8 is made of a metal
and the end of the conductive pin 4 located in the container 2
is welded to the central left end of the spring seat 8. The
cylindrical portion 8a formed on the right end of the spring seat
8 has an outer diameter substantially equal to the inner diameter
D2 of the coil spring 9. The proximal end of the coil spring
9 or a closely wound portion thereof is fitted with the
cylindrical portion 8a to be fixed to the latter by an
electrically conductive adhesive agent.
-
The coil spring 9 has the other end or free end having a
reduced diameter smaller than the diameter D1 of the sphere 10,
so that the sphere 10 is held in the-inner space of the coil spring.
More specifically, the free end of the coil spring 9 is closely
wound so as to be formed into a conical closely wound portion
9b. This portion serves as means for preventing the sphere 10
from falling off. Accordingly, the sphere 10 is previously
inserted through an opening at the proximal end 9a side into the
inner space of the coil spring 9 and thereafter, the coil spring
9 is fixed to the spring seat 8.
-
Thus, the coil spring 9 is cantilevered on the spring seat
8, and the sphere 10 is provided in the inner space of the coil
spring so as to be movable and comprises a plurality of steel
balls. As a result, the sphere 10 effectively functions as a
weight resiliently flexes the coil spring 9. The coil spring
9 is inclined downward relative to the horizontal axis in the
container 2 as shown in FIG. 1. The distal end of the coil spring
9 is normally in contact with the inner face of the container
2. The free fall sensor 1 having the above-described
construction is disposed on a conductive pattern (not shown) of
a printed circuit board 11 as shown by two-dot chain line in FIG.
1. A lead wire 12 is soldered to one end of the conductive pin
4 located outside the container 2. An L-shaped metal contact
13 is welded to the underside of the container 2, whereupon an
electrical path is formed so as to be conductive to the printed
circuit board 11.
-
The electrical path is normally formed as the result of
contact between the coil spring 9 and the container 2. The sphere
10 is adapted not to prevent the flexure of the coil spring 9.
The coil spring 9 with the inner space in which the sphere 10
is cantilevered functions as the movable electrode 5, whereas
the container 2 fixedly mounted on the printed circuit board 11
functions as a fixed electrode. The coil spring 9 and container
2 constitute a switching mechanism. The aforesaid printed
circuit board 11 is fixed inside the portable computer and
connected to a central processing unit (CPU; and not shown). A
conduction signal is supplied from the printed circuit board 11
to CPU when a section between the lead wire 12 and the contact
13 is electrically conductive.
-
The operation of the free fall sensor will now be described.
In a stationary or normal state, the central axis is substantially
horizontal as shown in FIG. 1, and the gravity of the sphere 10
elastically flexes the cantilevered beam-like coil spring 9 such
that the free end of the coil spring is in contact with the inner
surface of the container 2. Consequently, electric current
flows through the lead wire 12, conductive pin 4, the coil spring
9 with the sphere 10 enclosed in the inner space thereof (the
movable electrode 5), container 2 serving as the fixed electrode,
and the contact 13. Thus, the free fall sensor 1 serves as a
normally closed switch. An electrical path to the printed
circuit board 11 is thus formed, whereby the conduction signal
is supplied to CPU.
-
On the other hand, the coil spring 9 is disconnected from
the container 2 while the portable computer is in a falling state,
as shown in FIG. 2. More specifically, the gravity applied to
the sphere 10 is apparently reduced when the portable computer
is in the falling state. Accordingly, the coil spring 9 is
displaced by the spring force or elastic restoring force thereof
so as to be returned toward the central side of the container
2. When the gravity applied to the sphere 10 is reduced to zero
gravity, the free end of the coil spring 9 is completely parted
from the inner surface of the container 2, whereupon the section
between the lead wire 12 and the contact 13 is completely cut
off (OFF level).
-
CPU detects the OFF level of the conduction signal and
supplies an ABNORMAL STATE signal to an inner drive circuit (not
shown). The drive circuit is provided for driving a disk head
of an internal hard disk, for example. Upon detection of the
ABNORMAL STATE signal, the drive circuit moves the disk head to
a retreat position, thereby interrupting reading data and
program from the hard disk or writing data and program into the
hard disk. Thus, an evasive process is carried out to render
the possibility of damage to the data or disk head minimum.
-
Furthermore, a characteristic operation of the movable
electrode 5 will now be described with reference to FIGS. 4A to
5D. Necessary gravity is obtained from the sphere 10 comprising
five steel balls and serving as a weight in the embodiment. Since
the sphere 10 is allowed to be moved sufficiently particularly
in the direction of elongation of the coil spring 9 and is
spherical, the sphere has no such resistance as to prevent the
flexure of the coil spring. Moreover, the sphere 10 functions
as a core provided in the inner space of the coil spring 9, thereby
acting as a resistor effectively suppressing a large bending
resulting in buckling or plastic deformation of the coil spring.
-
The sphere 10 further has a damping action as shown in FIGS.
4A and 4B. FIG. 4C shows a prior art construction. The damping
action will now be described with reference to FIG. 4A. The
cantilevered coil spring 9 has a larger amount of downward elastic
deformation at the free end side than at the other portion thereof.
In order that a reliable contact with the container 2 may be
ensured, the sphere 10 comprising five steel balls are disposed
in the inner space of the coil spring 9, whereby required weight
is ensured. The coil spring 9 is cantilevered at the proximal
end thereof and the free end side thereof is brought into a sudden
contact or collides with the container 2. In this case, the
middle portion of the coil spring 9 is elastically deformed up
and down, thereby vibrating up and down as shown by arrow Y in
FIG. 4A. As a result, the shock due to collision can be received
so as to be dampened. Thus, a shock damping effect by the damping
action can be achieved. Moreover, since the free end of he coil
spring 9 is kept in contact with the inner face of the container
2, frequent bounce (repeated collision) can be prevented and
accordingly, the vibration can be reduced to a large extent.
-
Furthermore, the coil spring 9 constituting the movable
electrode 5 has the proximal end 9a closely wound and fixed to
the spring seat as shown in FIGS. 1 and 2. This can increase
the mechanical strength of the movable electrode 5 against the
shock in the falling and can diffuse the bending stress and the
like due to shock in the falling without concentration of the
bending stress and the like, thereby ensuring the flexibility.
Accordingly, plastic deformation and buckling can further be
prevented.
-
On the other hand, it is effective to fill the airtight
container 2 with, for example, nitrogen gas so that oxidation
can be prevented. However, an electrode surface of the contact
portion of the container 2 or coil spring 9 would be oxidated
or soiled by oxidation of the contact portion or soil before
filling of the nitrogen gas. As a result, there is a possibility
that stable conduction may not be achieved. In the embodiment,
however, every time the coil spring 9 collides with the container
2, an elastic expansion and contraction action in the direction
of elongation (shown by arrow X in FIG. 4B) as a characteristic
of the coil spring is achieved as well as the aforementioned
damping action. Consequently, a wiping effect is obtained that
a contact portion slides right and left when subjected to
vibration or shock due to the falling. Soil and an oxide film
on the contact face can be removed by the wiping effect.
Accordingly, the switching operation stable for a long period
of time can be realized even when the contact pressure of the
electrode tends to be reduced as the result of miniaturization
of the free fall sensor.
-
In the prior art construction as shown in FIG. 4C, a
cantilevered bar-shaped spring A is provided with a weight B of
steel ball. The weight B is brought into contact with a container
C at a point below the center of gravity G of the weight.
Accordingly, the single spring A is liable to be deformed due
to buckling as described above. Moreover, this tendency is more
conspicuous as the spring force is rendered small by reduction
in the diameter of the bar-shaped spring. Thus, the prior art
construction is unsuitable for reducing the spring force. As
a result, the weight B is restricted by miniaturization of the
free fall sensor. Moreover, since the weight B is brought into
contact with the container C at the point below the center of
gravity G of the weight, there is a possibility that a stable
conductive state may not be obtained when the contact faces are
soiled or oxidated by a long time of service. Thus, the prior
art construction is disadvantageous for further size reduction.
-
Further, in the embodiment, the conductive pin 4 is
connected to one of the ends of the spring seat 8 and the coil
spring 9 is connected to the other end of the spring seat when
the coil spring is cantilevered so as to be disposed in the form
of a beam. In this case, it is desirable that the conductive
pin 4, spring seat 8 and coil spring 9 should be connected linearly
on a horizontal central axis. In particular, a gap between the
coil spring 9 and the container 2 is reduced as the free fall
sensor becomes thinner or smaller in size. Further, the accuracy
in the central axis of the incorporated coil spring 9 is important
in order that a stable switching operation may be achieved
irrespective of a mounting angle (360 degrees). Yet, the coil
spring 9 is flexible and accordingly, it is not always easy to
align the coil spring 9 on a central axis.
-
In the embodiment, however, the central axis of the coil
spring 9 can easily be adjusted, whereupon the required assembly
accuracy can be ensured. With reference to FIGS. 5A to 5D, the
following describes means for adjusting the movable electrode
5. FIGS. 5A to 5D show an assembly comprising the conductive
pin 4 airtightly inserted through a hole 3a of the closing member
3 and the coil spring 9 including the spring seat 8 and sphere
10 constituting the movable electrode 5, that is, the assembly
which is to be force fitted into the container 2. FIGS. 5A and
5C show the assembly prior to adjustment, whereas FIGS. 5B and
5D show the assembly after adjustment. FIG. 5A shows the
assembly disposed vertically in the natural state, whereas FIG.
5C is a view as seen from the free end side of the coil spring
9 or in the direction of arrow B. FIG. 5B shows the assembly
disposed vertically in the natural state, whereas FIG. 5D is a
view as seen from the free end side of the coil spring 9 or in
the direction of arrow B.
-
When the central axis (shown by central line R0) of the
assembly is inclined slightly rightward at this assembly stage
as shown by symbol R1 in FIGS. 5A and 5C, the circular
outer-diameter portion of the coil spring 9 is eccentric relative
to the circular closing member 3. Accordingly, in what direction
the coil spring 9 is inclined can be visually confirmed readily.
Then, as shown in FIG. 5B, a suitable portion of the spring seat
8 is held by tweezers, for example, and is flexed slightly in
the direction of arrow E or F so that the inclination is corrected.
It is confirmed that the coil spring 9 has been adjusted to a
central position as shown in FIG. 5D. As a result, the coil
spring 9 can be disposed about the central axis, that is, the
movable electrode 5 can be disposed about the central axis.
Although the spring seat 8 is welded to the conductive pin 4 as
described above, the coil spring 9 is fitted with the cylindrical
portion 8a of the spring seat 8 thereby to be fixed, a slight
angular displacement of the spring seat B can realize the
aforesaid adjustment of central axis.
-
The assembly adjusted as described above is force-fitted
into the container 2 so that the free fall sensor is finally
completed. The free fall sensor of the embodiment can be
thickened to about 1 mm and can be practically usable although
the thickness of the conventional free fall sensor is has been
reduced to about 5 mm at the smallest.
-
The following effects can be achieved from the foregoing
embodiment. Since the container 2 serving as the fixed electrode,
the coil spring serving as the movable electrode 5 and the like
are each formed into a circular shape, the free fall sensor can
readily be incorporated into the equipment such as a portable
computer without limitation of a mounting angle. The free fall
sensor thus produced can detect the falling state of the equipment
by a normal switching operation, so that a quick countermeasure
can be taken.
-
Furthermore, the following are particularly eminent
characteristics of the free fall sensor of the embodiment.
Firstly, since the sphere 10 constituting the weight of the
movable electrode 5 is disposed in the inner space of the coil
spring 9, the sphere 10 prevents the coil spring 9 from
deformation when the coil spring is excessively bent. Thus, the
sphere 10 serves as a core for the coil spring 9. More
specifically, the sphere 10 effectively functions to restrain
such a large deformation as to result in the buckling or plastic
deformation of the coil spring 9 upon occurrence of shock due
to the falling. Further, since the coil spring 9 substantially
defines the outer diameter of the free fall sensor, the
construction is advantageous when the diameter of the sensor is
reduced so that the sensor is thinned. Further, the sphere 10
has a diameter smaller than the inner diameter of the coil spring
9 and the overall length L1 of the sphere is reduced, so that
the sphere 10 is movable in the direction of the free length
thereof. Consequently, nothing prevents the coil spring 9
serving as the movable electrode 5 from flexure.
-
Further, the weight comprises the sphere 10 further
comprising a plurality of steel balls. The sphere 10 can easily
be obtained by casting at low costs. Further, a plurality of
-steel balls employed as the sphere 10 are advantageous in
adjusting and setting the weight of the sphere. Moreover, the
free end of the coil spring 9 is closely wound so as to be formed
into a conical closely wound portion 9b serving as means for
preventing the sphere in the inner space of the coil spring 9
from falling off. Since the coil spring 9 can be prevented from
falling off by itself, other components or fixing means is
required and moreover, the proximal end of the coil spring 9
serving as the movable electrode 5 is easily joined to the spring
seat. As a result, the free fall sensor has an improved
assembling efficiency and high accuracy and is accordingly
further advantageous in the costs. Further, since the proximal
end of the coil spring 9 is closely wound, a sufficient bonding
strength can be obtained and the construction is resistant
against large shock in the falling and effective in preventing
the coil spring 9 from easily buckling.
-
Further, the movable electrode 5 comprises the coil spring
9 with the movable sphere 10 disposed in the inner space of the
coil spring. Accordingly, when the movable electrode 5 collides
with the container 2 serving as the fixed contact, the shock due
to collision can be received so as to be dampened. Thus, a shock
damping effect by the damping action can be achieved. More
specifically, it is conventionally the weight that collides
against the container but in the foregoing embodiment, the coil
spring 9 is interposed, whereupon the silencing effect can be
expected. Moreover, the middle portion of the coil spring
vibrates while the distal end of the coil spring is in contact
with the inner face of the container or kept in such a tendency.
Accordingly, the shock due to the falling is damped, and the
number of bound can be rendered minimum and a bounding distance
can be rendered small. Consequently, noise due to the collision
can effectively be reduced. Further, the chattering of the
switching function due to repeated contact and separation of the
electrodes can be reduced and accordingly, the possibility of
malfunction resulting from turn-off of the free fall sensor can
be avoided, for example.
-
The sound produced by the collision between the coil spring
9 and the container 2 may be an abnormal sound when the portable
computer incorporated with the free fall sensor as well as in
the falling. In this case, too, the damping action is effective,
thereby improving the product value. Further, the free end of
the coil spring 9 is closely wound into the conical closely wound
portion 9b, which portion is brought into contact with the
container 2. Accordingly, even when the portion 9b is repeatedly
caused to collide against the container 2 in the falling, a
sufficient strength can be ensured, and the sound due to the
collision is also reduced by the damping action.
-
Bending stress or the like is apt to be concentrated on
the vicinity of the junction of the proximal end 9a by the damping
action in the falling as well as in the normal stationary state.
In the foregoing embodiment, however, the compression coil
spring has flexibility and the closely wound portion thereof is
fixed via the spring seat 8 to the conductive pin 4. Consequently,
the stress can be diffused and the deformation due to buckling
can be prevented. Thus, the switching operation between the coil
spring 9 and the inner face of the container 2 can be maintained
in a stable state for a long period of time, whereby the
reliability of the sensor can be improved.
-
In the foregoing embodiment, the damping effect is obtained
from vertical expansion and contraction of the coil spring 9,
whereas the wiping effect is obtained from the effective use of
the lengthwise expansion and contraction as disclosed with
reference to FIG. 4B. More specifically, the free end of the
coil spring 9 slides right and left on the inner face of the
container 2 while in contact with the latter, whereby soil or
oxide film on each contact face is removed. This can provide
a stable switching operation for a long period of time and in
particular, this can wipe out the possibility of unstable
operation due to reduction in the contact pressure between the
electrodes for miniaturization of the sensor.
-
Further, a space around the coil spring 9 constituting the
movable electrode 5 is designed to be minimum in order that the
free fall sensor 1 may be miniaturized and particularly thinned.
For example, when the thickness of the sensor is not more than
1.7 mm, the space becomes several tenths mm wide. Accordingly,
the connection of the coil spring 9 to the conductive pin 4
requires linear connection on a horizontal central axis. Since
the coil spring 9 is connected directly to the conductive pin
4, there is no problem when the coil spring 9 constitutes the
movable electrode. However, the working efficiency is reduced
if a high accurate assembling work is required in connection of
the coil spring 9. Accordingly, it is desirable to be able to
adjust the axis of the coil spring 9 easily after fixation. In
the foregoing embodiment, since the spring seat 8 is interposed
between the conductive pin 4 and the coil spring 9, the axis of
the coil spring can be adjusted by a slight displacement of the
spring seat 8 supporting the coil spring as described above with
reference to FIGS. 5A to 5D.
-
Thus, the coil spring 9 can accurately be disposed as the
movable electrode 5. Accordingly, the coil spring 9 can suitably
be disposed in a narrow space in the container 2 for the thinning
of the sensor. Moreover, the falling state can accurately be
detected even when the coil spring 9 is incorporated in every
direction. As a result, the possibility of thinning the sensor
can be increased and the free fall sensor of the embodiment is
effective when the size and weight of the portable computer is
further reduced and in particular, when the portable computer
is rendered further thinner.
-
In the foregoing embodiment, the conical closely wound
portion 9b is formed as the means for prevent the sphere 10 from
falling off from the free end of the coil spring 9. However,
fall-off preventing means should not be limited to the above
construction but may be modified into various forms. Modified
forms of the fall-off preventing means will be described with
reference to FIGS. 6 to 10 (corresponding to second to second
to fourth embodiments- respectively). In the second to fourth
embodiments, identical or similar parts are labeled by the same
reference symbols as those in the foregoing embodiment and will
not be described. Only the difference between each of the second
to fourth embodiments and the first embodiment will be described.
-
FIGS. 6 to 8 illustrate the second embodiment of the
invention and correspond to FIGS. 1 to 3 in the first embodiment
respectively. The free fall sensor of the second embodiment has
substantially the same construction as that of the first
embodiment except the fall-off preventing means. More
specifically, the free end of the coil spring 9 is closely wound
but has a cylindrical shape, instead of the conical closely wound
portion 9b. The free end includes a bent terminal 9c formed by
bending the terminal radially. The bent terminal 9c extends
centrally thereby to divide the open end substantially into two
parts, whereupon the cylindrical opening is substantially closed.
Consequently, the sphere 10 is abutted against the bent terminal
9c thereby to be prevented from falling off. The free fall sensor
of the second embodiment has the same function as that of the
first embodiment and achieves the same effect as that of the
second embodiment.
-
FIG. 9 illustrates a third embodiment of the invention.
In each of the foregoing embodiment, the coil spring 9 is itself
machined so as to constitute the fall-off preventing means. In
the third embodiment, however, an electrically conductive
bonding agent 14 is applied to the coil spring 9 to constitute
the fall-off preventing means. More specifically, the free end
of the coil spring 9 is closely wound in the same manner as in
the foregoing embodiments and remains open. The bonding agent
14 is applied to the free end of the coil spring 9 so as to close
the opening and then hardened.
-
Consequently, the open free end of the coil spring 9 is
closed by the bonding agent 14 hardened into the shape of a film,
which serves to prevent the sphere 10 enclosed in the inner space
of the coil spring 9 from falling off. A sufficient amount of
the bonding agent is small since the inner diameter D2 of the
coil spring 9 is about 1.0 mm which is extremely small. Since
the coil spring 9 has an extremely small size, part of the bonding
agent may be forced out of the coil spring. However, since the
conductive bonding agent is employed as the bonding agent 14 in
the embodiment, electrical conduction to the container 2 cannot
be prevented. The electrical conductivity is not always
required although use of the conductive bonding agent has an
advantage as described above. Further, the open free end of the
coil spring 9 may or may not be completely closed by the bonding
agent 14.
-
FIG. 10 illustrates a fourth embodiment of the invention
and corresponds to FIG. 1. Two spring seats 8 are employed in
the fourth embodiment. Thus, the spring seats 8 are fitted in
the proximal and free ends of the coil spring 9 respectively.
More specifically, the coil spring 9 is cylindrical as in the
third embodiment. Both proximal and free ends of the coil spring
9 are closely wound. The proximal end of the coil spring 9 is
fixed to the conductive spring seat 8 and the free end of the
coil spring is fitted with the cylindrical portion 8a of the
spring seat 8 and fixed by conductive bonding agent. Further,
the sphere 10 includes steel balls with two different diameters.
For example, two steel balls 10a each having a larger diameter
and heavier than the others are disposed at the free end side,
whereas three steel balls 10b each having a smaller diameter and
lighter are disposed at the proximal end side in the inner space
of the coil spring. The other construction of the free fall
sensor is the same as that in the third embodiment.
-
The sphere 10 also functions as the core of the coil spring
9 in the falling, whereupon an excessive bending deformation of
the coil spring 9. Further, the spring seat 8 can be utilized
as the fall-off preventing means for the sphere 10. As a result,
no new components are added. Moreover, a unit including the coil
spring 9 and the sphere 10 can be realized. In the unit, the
sphere 10 is enclosed in the inner space of the coil spring so
as to be prevented from fall-off. As a result, the unit can
easily be handled in the storage or transfer. For example, the
unit can be welded to the conductive pin 4, and thus, the
construction with wide use in the assembly can be obtained.
-
Further, the metal spring seat 8 provided at the free end
side is subjected to the gravity of the sphere 10 thereby to be
brought into direct contact with the container 2. The contact
state of the rigid body is more satisfactory as compared with
the contact by the elastic coil spring or the contact via the
conductive bonding agent as described in the foregoing
embodiments. The spring seat 8 is advantageous in that it
functions as a movable contact for the movable contact. Moreover,
two of the five steel spheres serve as heavier balls each having
a larger diameter. These steel balls are disposed at the free
end side of the coil spring 9. This can result in a more reliable
contact between the coil spring serving as the movable electrode
5 and the container 2.
-
In the foregoing embodiments, the steel balls with
different diameters are used so as to have two different weights.
For example, however, two different materials may be employed
for the sphere 10 with the same diameter, instead. Further, the
number of steel balls may be set according to the specifications
of the coil spring 9 or modified.
-
FIG. 11 illustrates a fifth embodiment of the invention
and corresponds to FIG. 1. In the fifth embodiment, identical
or similar parts are labeled by the same reference symbols as
those in the first embodiment and will not be described. Only
the difference between the fifth and first embodiments will be
described.
-
The sphere 10 comprising the steel balls is employed as
the weight in the foregoing embodiments. In the fifth embodiment,
a sphere 15 made of a light-weight material such as plastics or
aluminum is employed and a fall-off preventing member 16
comprising another member which also serves as the weight is
provided. The sphere 15 and the fall-off preventing member 16
constitute the movable electrode 17. More specifically, the
sphere 15 functions as the core of the coil spring 9 but does
not function as the weight. Then, the fall-off preventing member
16 is attached to the free end of the coil spring 9 so as to serve
as the fall-off preventing member for the sphere 15. The
fall-off preventing member 16 comprises a conductive member with
a large weight. The fall-off preventing member 16 is formed into
a cylindrical shape and has at one end thereof a stepwise
small-diameter portion 16a. The closely wound free end of the
coil spring 9 is fitted with the small-diameter portion 16a and
fixed by the conductive bonding agent. The fall-off preventing
member 16 has a slightly larger outer diameter than the coil
spring 9. The required weight can readily be set by adjustment
of the length as well as the diameter.
-
The same effect is achieved from the fifth embodiment as
from the first embodiment. Further, since the weight is adjusted
by a single fall-off preventing member 16, the weight setting
can be carried out easier as compared with the first embodiment
in which a plurality of steel balls constitute the sphere 10.
Furthermore, the fall-off preventing member 16 also serves as
a contact of the movable electrode 17 which is brought into
contact with the container 2. Accordingly, reliable contact can
be achieved as compared with the first embodiment in which the
coil spring 9 is brought into contact with the container. As
a result, the fifth embodiment is superior to the first embodiment
since the reliably contact state can be achieved and functions
for a long period of time.
-
The fall-off preventing member sensor may become slightly
larger and the length thereof may be increased since the fall-off
preventing member serves as the weight. However, the sphere 15
in the fifth embodiment is not required to serve as the weight,
the increase in the length of the fall-off preventing member 16
can be restrained by the adjustment including the reduction in
the number and the diameter of steel balls together with the
adjustment of the coil spring 9. In particular, the length of
the fall-off preventing member 16 does not prevent the free fall
sensor from compactness by rendering it thinner. Further,
although the fall-off preventing member 16 which also serves as
the weight is employed in the embodiment, a dedicated fall-off
preventing member and a dedicated weight may be provided,
instead.
-
The invention should not be limited by the foregoing
embodiments -described with -reference to the drawings. For
example, the shape of the spring seat to which the proximal end
of the coil spring is fixed may be modified, or the shape of the
fall-off preventing means may be modified. Further, the
proximal and free ends of the coil spring are closely wound and
accordingly, advantageous in the strength. However, these ends
may be closely wound if necessary. Further, the number of steel
balls should not be limited to five but may be one or two. The
sphere should not be limited to steel balls. Further, the
materials for the sphere may have different masses. The weight
adjustment can be made by a sphere with the aforementioned
combined structure. For example, various combinations are
possible as alternatives so that the gravity becomes larger at
the coil spring side, and minute adjustment is possible. Further,
the weight may be provided on another member in order that the
sphere serving as the core may protect the coil spring against
shock. Thus, the invention may be modified without departing
from the scope thereof.
-
FIGS. 12 to 15 illustrate a sixth embodiment of the
invention. FIG. 12 is a sectional view of the free fall sensor
1, showing the normal state in use (stationary state), and FIG.
13 is a view similar to-FIG.- 1, showing another operating state
of the free fall sensor in the falling. The construction of the
free fall sensor will be described with reference to FIGS. 12
and 13.
-
The free fall sensor 101 is provided, for example, in a
portable computer (not shown) such as a notebook-sized personal
computer in an oblong state as shown in FIG. 12. The free fall
sensor 101 comprises a slender cylindrical container 102 having
an opening at one end, a closing member 103 for closing the opening
of the container for electrical insulation and airtightness, an
electrically conductive pin 104 extending in an airtight manner
through the closing member 103 into the container 102, and a
movable electrode 105 fixed to an end of the conductive pin 104
inside the container. More specifically, the container 102 is
made of an electrically conductive metal and formed into the
slender cylindrical shape with the one open end (the left end
as viewed in FIG. 12). The conductive container 102 serves as
a fixed electrode as will be described later.
-
The closing member 103 comprises a cylindrical frame 106
and an electrically conductive filler 107, such as glass, filling
the interior of the frame. The conductive pin 104 extends
horizontally through a centrally located through hole 103a
formed in the bottom of the closing member 103. The frame 106
is force-fitted into the container 102 thereby to be fixed to
the latter. Before the force-fitting, an inner peripheral
surface of the container 102 and an outer peripheral surface of
the frame 106 are electroplated with nickel and gold or gold alloy.
Electroplated layers of the container 102 and frame 106 are
integrated together as together as the result of force fitting, whereupon
the airtightness is improved. The container 102 is airtightly
closed and the conductive pin 104 is electrically insulated from
the container 102. With this, the interior of the container 102
is evacuated or filled with an antioxidant gas such as gaseous
nitrogen or gaseous helium in order that the inner peripheral
surface of the container 102 serving as the fixed electrode may
be prevented from oxidation for a long period of time.
-
The movable electrode 105 is disposed in the container 102
closed as described above. The movable electrode 105 is
electrically brought into contact with and parted from the
container 102 in subjection to fall, shock or the like. An
electrically conductive disc-shaped spring seat plate 108 and
an oblong compression coil spring 109 are coupled in turn to the
end of the conductive pin 104 inside the container 102. A weight
110 serving as a weight is provided in an inner space of the coil
spring 109. More specifically, the spring seat plate 108 is made
of a metal and formed into the shape of a circular dish. The
central rear of the spring seat plate 108 is welded to the
conductive pin 104. The coil spring 109 is fixed by an
electrically conductive bonding agent to a receiving dish-shaped
side of the seat plate 108. The dish-shaped portion of the seat
plate 108 has an inner diameter substantially equal to the outer
diameter of the coil spring 109 and receives one end of the coil
spring 109. The coil spring 109 is made of an electrically
conductive metal such as phosphor bronze and includes a portion
fixed to the seat plate 108 and serving as a closely wound portion
109a relative to a middle coarsely wound portion.
-
The other or free end of the coil spring 109 is also formed
into a closely wound portion 109b, to which portion one end of
the weight 110 is fixed. The weight 110 is made of an
electrically conductive metal such as copper and formed into an
oblong cylindrical member with a silver-plated surface. The
weight 110 has a length substantially twice as large as the
diameter thereof or above and an outer diameter substantially
equal to (strictly, slightly-larger than) an outer diameter of
the coil spring 109. The end of the weight 110 connected to the
coil spring 109 is formed with a columnar mount 110a having a
slightly smaller diameter. The mount 110a has an outer diameter
substantially equal to an inner diameter of the coil spring 109.
The closely wound portion 109b of the coil spring 109 is fitted
with the mount 110a and fixed by the conductive bonding agent.
-
Thus, the coil spring 109 is cantilevered on the spring
seat 108, and the weight 110 is inclined downward relative to
the horizontal axis in the container 102 and the distal end
thereof is normally in contact with the inner face of the
container 102 as shown in FIG. 12. The free fall sensor 101
having the above-described construction is disposed on a
conductive pattern (not shown) of a printed circuit board 111
as shown by two-dot chain line in FIG. 12. A lead wire 112 is
soldered to one end of the conductive pin 104 located outside
the container 102. An L-shaped metal contact 113 is welded to
the underside of the container 102, whereupon an electrical path
is formed so as to be conductive to the printed circuit board
111.
-
The electrical path is normally formed as the result of
contact between the coil spring 109 and the container 102. The
coil spring 109 and weight 110 constitute a movable electrode
105, whereas the container 102 serves as a fixed electrode,
whereupon the coil spring 109, weight 110 and container 102
constitute a switching mechanism. The aforesaid printed circuit
board 111 is fixed inside the portable computer and connected
to CPU (not shown). A conduction signal is supplied from the
printed circuit board 111 to CPU when a section between the lead
wire 112 and the contact 113 is electrically conductive.
-
The operation of the free fall sensor will now be described.
In a stationary or normal state, the central axis is substantially
horizontal as shown in FIG. 1, and the gravity of the weight 110
elastically flexes the cantilevered beam-like coil spring 109
such that the free end of the coil spring is in contact with the
inner surface of the container 102. Consequently, electric
current flows through the lead wire 112, conductive pin 104,
movable electrode 105 (coil spring 109 and weight 110), container
102 serving as the fixed electrode, and the contact 113. Thus,
the free fall sensor 101 serves as a normally closed switch. An
electrical path to the printed circuit board 111 is thus formed,
whereby the conduction signal is supplied to CPU.
-
On the other hand, the weight 110 is disconnected from the
container 102 while the portable computer is in a falling state,
as shown in FIG. 13. More specifically, the gravity applied to
the weight 110 is apparently reduced when the portable computer
is in the falling state. Accordingly, the coil spring 109 is
displaced by the spring force or elastic restoring force thereof
so as to be returned toward the central side of the container
102. -When the gravity applied to the weight 110 is reduced to
zero gravity, electric current is cut off between the lead wire
112 and the contactor 113, whereupon supply of the conduction
signal from the printed circuit board 111 is stopped.
-
CPU usually monitors the conduction signal from the printed
circuit board 111. Upon detection of stop of the conduction
signal, CPU supplies an ABNORMAL STATE signal to an inner drive
circuit (not shown). The drive circuit is provided for driving
a disk head of an internal hard disk, for example. Upon detection
of the ABNORMAL STATE signal, the drive circuit moves the disk
head to a retreat position, thereby interrupting reading data
and program from the hard disk or writing data and program into
the hard disk. Thus, an evasive process is carried out to render
the possibility of damage to the data or disk head minimum.
-
The following effect can be achieved from the
above-described free fall sensor 101. Firstly, the weight 110
is formed into an oblong cylindrical shape and has the length
set to a value substantially twice as large as the diameter
thereof or above. Accordingly, even when the diameter of the
weight 110 is reduced, necessary mass can be ensured. Moreover,
since the weight 110 is connected to the coil spring 109 in the
direction of the length of the latter, the free fall sensor can
be set at a minimum thickness in the aforementioned electrode
arrangement. Further, the container 102 of the free fall sensor
101 has a cylindrical shape and the movable electrode 105
comprising the coil spring 109 and weight 110 also has a circular
shape. Accordingly, the free fall sensor can be disposed freely.
Moreover, the seat plate 108, coil spring 109 and weight 110 are
sequentially connected to the conductive pin 104 so as to confront
one another each in the circular shape. As a result, these
components can be assembled easily without any directional
limitation and the aforementioned arrangement is effective in
improving the designing and manufacturing efficiencies.
-
The operations as shown in FIGS. 14A to 14C will be
described. FIGS. 14A and 14B show the embodiment of the
invention, whereas FIG. 14C shows a prior art construction.
Firstly, as shown in FIG. 14A, the oblong weight 110 constitutes
a distal end of the coil spring. The center of gravity G is spaced
away from a point of contact with the container 102. The other
end of the weight 110 is fixed to the coil spring 109.
Accordingly, the weight 110 vibrates up and down in the direction
of arrow Y in FIG. 14A as the result of vertical elastic
deformation of the coil spring 109 when suddenly colliding
against the container 102, whereupon the shock can be received
by the weight 110. Thus, a shock damping effect by the damping
action can be achieved. Moreover, since the distal end of the
weight 110 is kept in contact with the inner face of the container
102, frequent bound (repeated collision) can be prevented.
-
Further, the bending stress or the like is apt to be
concentrated in the vicinity of a connection base between the
coil spring 109 and the cantilevered conductive pin 104 and in
the vicinity of the connection base between the coil spring 109
and the weight 110, whereupon there is a possibility of
deformation due to buckling. On the other hand, in the
embodiment, the closely wound portion 109b of the coil spring
109 is provided on the connection base. Accordingly, the
flexibility is maintained even when a large vibration occurs in
the vicinity of the connection base, and the gravitational force
of the weight and the bending stress in the occurrence of shock
due to the falling can be diffused by the closely wound portion.
As a result, the possibility of buckling deformation can be
prevented. This results in a reduction in the diameter of the
coil spring 109. Thus, the spring force can be reduced and the
size of the weight can also be reduced. Consequently, the
movable electrode 105 and accordingly, the free fall sensor 101
can be thinned.
-
Further, referring to FIG. 14B, the airtight container 102
is filled with nitrogen gas. However, the inner face of the
container 102 and the electrode surface of the weight 110 are
sometimes oxidated or soiled as the result of a long time of
service, whereupon there is a possibility that a stable
conduction may not be achieved. In the embodiment, however,
every time the weight 110 collides with the container 102, an
elastic expansion and contraction action in the direction of
elongation (shown by arrow X in FIG. 14B) as a characteristic
of the coil spring 109 is achieved as well as the aforementioned
damping action. Consequently, a wiping effect is obtained that
the weight 110 slides right and left when subjected to vibration
or shock due to the falling. Soil and an oxide film on the contact
face can be removed by the wiping effect. Accordingly, the
switching operation stable for a long period of time can be
realized even when the contact pressure of the electrode tends
to be reduced as the result of miniaturization of the free fall
sensor.
-
In the prior art constuction as shown in FIG. 14C, a
cantilevered bar-shaped spring A is provided with a weight B of
steel ball. The weight B is brought into contact with a container
C at a point below the center of gravity G of the weight.
Accordingly, the single spring A is liable to be deformed due
to buckling as described above. Moreover, this tendency is more
conspicuous as the spring force is rendered small by reduction
in the diameter of the bar-shaped spring. Thus, the prior art
construction is unsuitable for reducing the spring force. As
a result, the weight B is restricted by miniaturization of the
free fall sensor. Moreover, since the weight B is brought into
contact with the container C at the point below the center of
gravity G of the weight, there is a possibility that a stable
conductive state may not be obtained when the contact faces are
soiled or oxidated by a long time of service. Thus, the prior
art construction is disadvantageous for further size reduction.
-
Further, in the embodiment, the coil spring 109 is
connected via the spring seat plate 108 to the conductive pin
104 when cantilevered so as to be disposed in the form of a beam.
In this case, it is desirable that the conductive pin 104, spring
seat plate 108 and coil spring 109 should be connected linearly
on a horizontal central axis. In particular, the coil spring
109 is flexible and accordingly, it is not always easy to align
the coil spring 109 on a central axis. However, a gap between
the coil spring 109 and the container 102 is reduced as the free
fall sensor becomes thinner or smaller in size. Accordingly,
a high assembly accuracy and strict dimensional control are
required in order that a stable switching operation may be
achieved.
-
Means will be described for adjusting so that the movable
electrode 105 is linearly connected on the central axis with
reference to FIGS. 15A to 15D. FIGS. 5A to 5D show an assembly
comprising the conductive pin 104 airtightly inserted through
the closing member 103, the spring seat plate 108, the coil spring
109 and weight 110. The assembly is to be force fitted into the
container 102. FIGS. 15A and 15C show the assembly prior to
adjustment, whereas FIGS. 5B and 5D show the assembly after
adjustment. FIG. 15A shows the assembly disposed vertically in
the natural state, whereas FIG. 15C is a view as seen from the
free end side of the coil spring 109 or in the direction of arrow
B. FIG. 15B shows the assembly disposed vertically in the
natural state, whereas FIG. 15D is a view as seen from the free
end side of the coil spring 109 or in the direction of arrow A.
-
When the central axis (shown by central line R0) of the
assembly is inclined slightly rightward at this assembly stage
as shown by symbol R1 in FIGS. 15A and 15C, the circular
outer-diameter portion of the weight 110 is eccentric.
Accordingly, in what direction the weight 110 is inclined can
be visually confirmed readily. Then, as shown in FIG. 15B, a
suitable portion of the spring seat plate 108 is held by tweezers,
for example, and is flexed slightly in the direction of arrow
C or B so that the inclination is corrected. It is then confirmed
that the weight 110 has been adjusted to a central position as
shown in FIG. 15D. As a result, the coil spring 109 can be
disposed about the central axis, that is, the movable electrode
105 can be disposed about the central axis. Although the spring
seat plate 108 is welded to the conductive pin 104 as described
above, the coil spring 109 is fitted with the spring seat plate
108 thereby to be fixed, a slight angular displacement of the
spring seat plate 108 can realize the aforesaid adjustment of
central axis.
-
The assembly adjusted as described above is force-fitted
into the container 2 so that the free fall sensor is finally
completed. The free fall sensor 101 of the embodiment can be
thickened to about 1 mm or below 1 mm and can be practically usable
although the thickness of the conventional free fall sensor is
has been reduced to about 5 mm at the smallest. This corresponds
to an outer diameter of the container 102. An experiment was
conducted to confirm operability of the assembly with the
following component specifications, and the assembly was found
to be realizable.
Component specifications of free fall sensor
-
Coil spring 109: compression coil spring (made of copper)
Length: 1.7 to 3.0 mm
Outer diameter: 0.4 to 0.8 mm
Wire size: 30 µm
Weight 110: Circular column (made of copper)
Length: 1.5 to 2.5 mm
Diameter: 0.6 to 1.0 mm
-
The following effects can be achieved from the foregoing
embodiment. Since the container 102 serving as the fixed
electrode, the coil spring 109 serving as the movable electrode
105 and the like are each formed into a circular shape, the free
fall sensor can readily be incorporated into the equipment such
as a portable computer without limitation of a mounting angle.
The free fall sensor thus produced can detect the falling state
of the equipment by a normal switching operation, so that a quick
countermeasure can be taken.
-
Furthermore, the following are particularly eminent
characteristics of the free fall sensor of the embodiment.
Firstly, since the weight 110 is oblong, necessary mass can be
achieved even though the weight has a reduced diameter. Moreover,
since the weight 110 is connected in the direction of elongation
of the coil spring 109, the weight 110 can be set at a minimum
thickness, thereby contributing to further reduction in the
thickness of the sensor.
-
Additionally, the movable electrode 105 comprises the coil
spring 109 and the oblong weight 110. Accordingly, the damping
effect can be expected that the shock can be received to be damped
when the weight 110 collides against the container 102, as
described with reference to FIG. 14A. Consequently, sound due
to the collision of the weight 110 against the container 102 can
be reduced, and the weight 110 is retained in the state where
the distal end thereof shifted from the center of gravity G is
kept in contact with the inner face of the container 102, or even
if the weight is bounded, the number of bounding is small and
the bounding is restrained to a slight distance. As a result,
noise due to collision can effectively be reduced. Further,
since almost no contact and separation between the electrodes
occur, chattering of the switching function can be prevented.
For example, malfunction due to turn-off can be avoided.
Additionally, there is a possibility that the sound due to the
collision of the weight 110 against the container 102 may become
a noise when the portable computer is carried as well as in the
falling. Accordingly, the effect by the damping improves the
product value.
-
Bending stress or the like is apt to be concentrated on
the vicinity of the junction of the proximal end 109a by the
damping action in the falling as well as in the normal stationary
state. In the foregoing embodiment, however, the compression
coil spring has flexibility and the fixing bases serving as the
closely wound portions 109a and 109b are fixed to the conductive
pin 104 and the weight 110 respectively. Consequently, the
stress can be diffused and the deformation due to buckling can
be prevented. Thus, the switching operation between the weight
110 and the container 102 can be maintained in a stable state
for a long period of time, whereby the reliability of the sensor
can be improved. Further, since the wire diameter of the coil
spring 1 can be reduced, the spring force can be reduced and the
mass of the weight 110 can be reduced. As a result, further
miniaturization of the free fall sensor can be carried out. In
this case, since the spring force and the size of the weight 110
can be reduced and the whole sensor can be rendered smaller, noise
due to the collision of the weight 110 against the container 102
can also be reduced effectively.
-
In the foregoing embodiment, the damping effect is obtained
from vertical expansion and contraction of the coil spring 109,
whereas the wiping effect is obtained from the effective use of
the lengthwise expansion and contraction as disclosed with
reference to FIG. 14B. More specifically, the weight 110 slides
right and left on the inner face of the container 102 while in
contact with the latter, whereby soil or oxide film on each
contact face is removed. This can provide a stable switching
operation for a long period of time and in particular, this can
wipe out the possibility of unstable operation due to reduction
in the contact pressure between the electrodes for
miniaturization of the sensor.
-
Further, a space around the movable contact 105 in the
container 102 is designed to be minimum in order that the free
fall sensor 101 may be miniaturized and particularly thinned.
For example, when the thickness of the sensor is not more than
1.7 mm, the space becomes several tenths mm wide. Accordingly,
the connection of the coil spring 109 and the weight 110 to the
conductive pin 104 requires linear connection on a horizontal
central axis. Since the coil spring 109 is connected directly
to the conductive pin 104, there is no problem. However, the
working efficiency is reduced if a high accurate assembling work
is required in connection of the coil spring 109. Accordingly,
it is desirable to be able to adjust the axis of the coil spring
109 easily after fixation. In the foregoing embodiment, since
the spring seat plate 108 is interposed between the conductive
pin 104 and the coil spring 109, the axis of the coil spring can
be adjusted by a slight displacement of the spring seat plate
108 supporting the coil spring as described above with reference
to FIGS. 15A to 15D.
-
Thus, the coil spring 109 can accurately be disposed as
the movable electrode 105. Accordingly, the coil spring 109 can
suitably be disposed in a narrow space in the container 102 for
the thinning of the sensor. Moreover, the falling state can
accurately be detected even when the coil spring 109 is
incorporated in every direction. As a result, the possibility
of thinning the sensor can be increased and the free fall sensor
of the embodiment is effective when the size and weight of the
portable computer is further reduced and in particular, when the
portable computer is rendered further thinner.
-
FIGS. 16A to 16D illustrate seventh and eighth embodiments
of the invention. Identical or similar parts in the seventh and
eighth embodiments are labeled by the same reference symbols as
those in the sixth embodiment. The seventh and eighth
embodiments relate to improvements in the means for mounting the
free fall sensor 101 on the printed circuit board 111. FIGS.
16A and 16B show the seventh embodiment and FIGS. 16C and 16D
show the eighth embodiment.
-
For example, in the seventh embodiment, the free fall
sensor 101 is connected via a lead 112 between the conductive
pin 104 and the printed board 111 and further connected via a
contact 113 to the container 102 and printed board 111. When
the sensor is soldered to the printed board 111, a mounting
direction is limited.
-
On the other hand, in each of the seventh and eighth
embodiments, the sensor can easily be connected to the printed
board 111 without limitation of the mounting direction. Firstly
in the seventh embodiment as shown in FIGS. 16A and 16b, a lead
disc 114 made of a metal is welded to an outer end of the conductive
pin 104. FIG. 16B is a view as viewed in the direction of arrow
D. The lead disc 114 has an outer diameter substantially equal
to that of the container 102. The conductive pin 104 is connected
to the center of a circular flat face so as to be electrically
conductive.
-
The free fall sensor 101 and the lead plate 114 have
substantially the same outer diameter and accordingly, the free
fall sensor can be disposed on the printed board 111 without
limitation of the mounting direction. As a result, the lead
plate 111 and the container 102 serving as the fixed electrode
are soldered at solders 115 and 116 to corresponding positions
of the conductive pattern (not shown) of the printed board 111,
whereupon predetermined electrical paths are formed. Thus, in
addition to the construction of the nondirectional free fall
sensor, means for electrically connecting the free fall sensor
to the printed board 111 is not limited in the directionality.
As a result, the assembling efficiency can be improved to a large
extent, and the circular lead disc 114 is not limited in the
directionality, whereupon the connection to the conductive pin
104 can be easily carried out. In this respect, the free fall
sensor can efficiently be assembled.
-
On the other hand, in the eighth embodiment as shown in
FIG. 16B, a metal polygonal or, for example, square lead plate
117 is welded to an outer end of the conductive pin 104. The
lead plate 117 has an outer dimension substantially equal to the
outer diameter of the container 102. The conductive pin 104 is
connected to a central portion of the square lead plate 117. The
conductive pin 104 is connected to the center of a circular flat
face so as to be electrically conductive.
-
According to the forgoing construction the free fall
sensor can easily be connected at four points to the printed board
111 although the eighth embodiment does not reach the seventh
embodiment in which the directionality of the lead plate 114 has
no stages. Consequently, the assembling efficiency
substantially the same as in the seventh embodiment can be
achieved from the eighth embodiment.
-
The invention should not be limited to the foregoing
embodiments as described with reference to the accompanying
drawings. For example, the fixing means provided at both ends
of the coil spring and the spring seat plate should not be limited
to the above-described dish-shaped one. The spring seat plate
may have a shape of sheet to which the end face of the coil spring
is adjacent, or another engaging means serving as positioner may
be provided. Further, two free fall sensors may be provided so
that the falling state in every direction can reliably be detected.
Thus, the present invention may be modified without departing
from the scope thereof.
-
FIGS. 17 and 18 illustrate a ninth embodiment of the
invention. The free fall sensor 201 comprises a slender
cylindrical container 202 having an opening at one end, a closing
member 203 for closing the opening of the container for electrical
insulation and airtightness, a bar-shaped electrically
conductive pin 204 extending in an airtight manner through the
closing member 203 into the container 202, and a movable electrode
205 connected to an inner end of the conductive pin 204 inside
the container 202.
-
More specically, the container 202 is made of an
electrically conductive metal and has one open end and a closed
end. The conductive container 202 serves as a fixed electrode
as will be described later. Next, the closing member 203
comprises a cylindrical frame 206 and an electrically conductive
filler 207, such as glass, filling the interior of the frame.
The conductive pin 204 extends horizontally through a centrally
located through hole 203a formed in the bottom of the closing
member 203. The frame 206 is force-fitted into the container
202 thereby to be fixed to the latter. In this case, an inner
peripheral surface of the container 2 and an outer peripheral
surface of the frame 6 are previously electroplated with nickel
and gold or gold alloy M. Electroplated layers of the container
2 and frame 6 are integrated together as the result of
force-fitting, whereupon the airtightness is improved.
-
The container 202 is airtightly closed and the conductive
pin 204 is electrically insulated from the container 202. With
this, the interior of the container 202 is evacuated or filled
with an antioxidant gas such as gaseous nitrogen or gaseous helium
in order that the inner peripheral surface of the container 202
serving as the fixed electrode may be prevented from oxidation
for a long period of time.
-
The specific construction of the movable electrode 205 will
now be described. The movable electrode 205 is disposed in the
container 202 closed as described above. The movable electrode
205 is electrically brought into contact with and parted from
the container 202 in subjection to fall, shock or the like. The
movable electrode 205 comprises a coil spring 209 and a weight
210 both connected via the conductive joint 208 to the inner end
of the conductive pin 204 in turn so that the coil spring and
weight are electrically conductive. More specifically, the
joint 208 is made of a metal and formed into the shape of a circular
shallow dish. The central rear of the standing joint 208 is
welded to an inner end of the conductive pin 204. The joint 208
may or may not be provided in the embodiment. Accordingly, the
coil spring 209 may directly be connected to the conductive pin
204. However, the joint 208 is useful in that the joint makes
it easier to connect the coil spring 209 and to adjust for
improvement in the assembly accuracy of the movable electrode
205.
-
The coil spring 209 is connected to a receiving dish-shaped
face side of the joint 208 by an electrically conductive bonding
agent. The joint 208 has an inner diameter substantially equal
to an outer diameter of the coil spring 209 and receives one end
of the coil spring 209. The coil spring 209 comprises a
compression coil spring made of an electrically conductive metal
such as phosphor bronze or the like and formed into a cylindrical
shape. The coil spring 9 has an end which is to be fixed to the
joint 208 and formed into a force-fit closely wound portion 209a
with improved rigidity. As a result, the bonding work can be
simplified and the telescopic motion of the closely wound portion
209a is canceled so that the original flexure is not influenced
by the application of the bonding agent.
-
The coil spring 209 is thus cantilevered via the joint 208
on the conductive pin 204 and has the other or free end connected
to the weight 210. The free end of the coil spring 209 is also
formed with a closely wound portion 209b having a predetermined
length. The closely wound portion 209b is fixed to one end of
the weight 210 by the conductive bonding agent. The weight 210
is made of an electrically conductive metal such as copper and
formed into an oblong columnar shape. The weight 210 has a
surface which is silver-plated. The weight 210 has a diameter
slightly larger than an outer diameter of the coil spring 209.
The weight 210 has one end connected to the coil spring 209 and
a core member 211 integrally formed at the one end side. The
core member 211 has a diameter smaller than the inner diameter
of the coil spring 209 and is formed into a circular cylindrical
shape. The core member 211 is loosely inserted into the inner
space of the coil spring 209.
-
The coil spring 209 has an effective length L0 which
excludes both closely wound portions 209a and 209b and
corresponds to a free wound portion. The core member 211 has
a length L1 slightly shorter than the effective length L0 of the
coil spring 209 (L0>L1). Accordingly, the coil spring 209 is
designed to flex at a stroke S corresponding to a predetermined
dimension which is equal at least to the difference between L0
and L1. Further, in the embodiment, the coil spring 209 is
capable of flexing until the distal end of the core member 211
reaches the closely wound portion 209a to be blocked by the joint
208. Since the core member 211 is thus set at the length L1
shorter than the effective length L0 of the coil spring 209, an
amount of flexure is ensured which is required for the core member
211 to be blocked by the member at the conductive pin side even
though the closely wound portion 209a is filled with the bonding
agent.
-
The free fall sensor 201 thus assembled is incorporated
in the portable computer (not shown) such as a notebook-sized
personal computer in an oblong state as shown in FIG. 18. In
this case, the coil spring 209 is cantilevered and the weight
210 is connected to the free end of the coil spring 209.
Accordingly, the coil spring 209 is flexed to a larger extend
at the weight 210 side such that the weight 210 side of the coil
spring is inclined below the horizontal central axis in the
container 202. The coil spring 209 is normally maintained in
the state where the distal end of the weight 210 is in contact
with the inner face of the container 202 as shown in FIG. 18.
In this case, the core member 211 is loosely inserted in the inner
space of the coil spring 209 so that the coil spring 209 is allowed
to flex.
-
The free fall sensor 201 having the above-described
construction is disposed on a conductive pattern (not shown) of
a printed circuit board 212 of the equipment. A lead wire 213
is soldered to an outer end of the conductive pin 204 located
outside the container 202, for example. An L-shaped metal
contact 214 is welded to the underside of the container 202,
whereupon an electrical path is formed so as to be conductive
to the printed circuit board 212.
-
Accordingly, the electrical path is normally formed as the
result of contact between the weight 210 and the container 202
The coil spring 209 and weight 210 both connected to the
conductive pin 204 constitute a movable electrode 205, whereas
the container 202 serves as a fixed electrode, whereupon the coil
spring 209, weight 210 and container 202 constitute a switching
mechanism. The aforesaid printed circuit board 212 is fixed
inside the portable computer and connected to CPU (not shown).
A conduction signal is supplied from the printed circuit board
212 to CPU when a section between the lead wire 213 and the contact
214 is electrically conductive.
-
The operation of the free fall sensor will now be described.
In a stationary or normal state, the central axis is substantially
horizontal as shown in FIG. 18, and the gravity of the weight
210 elastically flexes the cantilevered beam-like coil spring
209 such that the free end of the coil spring is in contact with
the inner surface of the container 202. Consequently, electric
current flows through the lead wire 213, conductive pin 204,
movable electrode 205 (coil spring 209 and weight 210), container
202 serving as the fixed electrode, and the contact 214. Thus,
the free fall sensor 201 serves as a normally closed switch. An
electrical path to the printed circuit board 212 is thus formed,
whereby the conduction signal is supplied to CPU.
-
On the other hand, a case where the portable computer has
fallen will now be described. The gravity applied to the weight
210 is apparently reduced when the portable computer is in the
falling state. Accordingly, the coil spring 209 is displaced
by the spring force or elastic restoring force thereof so as to
be returned toward the central side of the container 202,
whereupon the coil spring 209 is parted from the container 202.
When the gravity applied to the weight 210 is reduced to a
predetermined value, the distal end of weight 210 at the free
end side is completely parted from the inner face of the container
202 as shown in FIG. 17, whereupon electric current is cut off
between the lead wire 213 and the contact 214, where upon supply
of the conduction signal from the printed circuit board 212 is
stopped.
-
CPU usually monitors the conduction signal from the printed
circuit board 212. Upon detection of stop of the conduction
signal, CPU supplies an ABNORMAL STATE signal to an inner drive
circuit (not shown). The drive circuit is provided for driving
a disk head of an internal hard disk, for example. Upon detection
of the ABNORMAL STATE signal, the drive circuit moves the disk
head to a retreat position, thereby interrupting reading data
and program from the hard disk or writing data and program into
the hard disk. Thus, an evasive process is carried out to render
the possibility of damage to the data or disk head minimum.
-
The free fall sensor 201 undergoes large shock or rebound
when fallen onto a floor, for example. In particular, the weight
210 connected to the coil spring 209 is movable in the compressing
direction of the coil spring although the interior of the
container 202 is narrow. Accordingly, there is conventionally
a possibility that a part of the coil spring 209 may be plastically
deformed when the coil spring 209 undergoes sudden compression
resulting in total contraction.
-
On the other hand, in the embodiment, the core member 211
with the smaller diameter is loosely inserted in the inner space
of the coil spring 209, and the length L1 of the core member 211
is set to be shorter than the effective length L0 of the coil
spring 209 (L0>L1). The core member 211 is incorporated so as
to be displaceable by compression at least a predetermined
dimension S until the distal end of the core member is blocked
by the joint 8 as the member at the conductive pin 204 side in
order that minimum expansion and contraction may be ensured.
Accordingly, when the sensor undergoes relatively small shock,
the weight 210 is parted from the container 202 by the elastic
deformation of the coil spring 209 with the effective length L0,
the supply of the conduction signal is stopped. Further, the
aforementioned evasive process is carried out. Thus, a large
flexure causing plastic deformation of the coil spring 209 can
be coped with without function of the core member 211. On the
other hand, upon occurrence of large shock, the core member 211
is moved a distance corresponding to the dimension S and
thereafter, blocked by the member of the conductive pin 204 side.
As a result, the movement of the weight 210 is prevented such
that large flexure of the coil spring 209 can be restrained,
whereby the coil spring 209 is prevented from plastic deformation.
In this case, since the weight 210 is limited to a slight
displacement, sound due to collision against the container 202
and rebound can also be reduced. Thus, the core member 211 limits
an amount of displacement of the coil spring 209 in the
compressing direction to a predetermined range, thereby serving
as displacement limiting means for limiting displacement of the
coil spring 209.
-
Further, the oblong weight 210 is brought into contact with
the container 202 at the distal end thereof spaced from the center
of gravity. Accordingly, the cantilevered coil spring 209
undergoes vertical elastic deformation by vibration, thereby
vibrating vertically within a range of space where it radially
abuts against the core member 211, as shown by arrow Y in FIG.
18. As a result, the vibration is received so as to be damped,
whereby a shock damping effect due to the damping action can be
obtained. In this case, the contact between the distal end of
the weight 210 and the container 202 is maintained, so that at
least frequent bounding (chattering) is reduced to a large
extent.
-
Additionally, in the embodiment, the airtight container
202 is filled with nitrogen gas. However, the inner face of the
container 202 and the electrode surface of the weight 210 are
sometimes oxidated or soiled as the result of a longtime of
service, whereupon there is a possibility that a stable
conduction may not be achieved. In the embodiment, however,
every time the weight 210 collides with the container 202, an
elastic expansion and contraction action in the direction of
elongation (shown by arrow X in FIG. 18) as a characteristic of
the coil spring 209 is achieved as well as the aforementioned
damping action. Consequently, a wiping effect is obtained that
the weight 210 slides right and left when subjected to vibration
or shock due to the falling. Soil and an oxide film on the contact
face can be removed by the wiping effect. Accordingly, the
switching operation stable for a long period of time can be
realized even when the contact pressure of the electrode tends
to be reduced as the result of miniaturization of the free fall
sensor.
-
The closely wound portions 209a and 209b of the coil spring
209 is effective in rendering the connecting work easier when
the joint 208 and weight 210 are connected to the coil spring
by the bonding agent, as described above. Further, the bending
stress or the like is apt to be concentrated in the boundary
between these connection bases and the vibrating portions,
whereupon there is a possibility of plastic deformation. On the
other hand, in the embodiment, the closely wound portions 209a
and 209b of the coil spring 209 are provided on the connection
base. Accordingly, the flexibility is maintained even when a
large vibration occurs in the vicinity of the connection bases,
and the gravitational force of the weight and the bending stress
in the occurrence of shock due to the falling can be diffused
by the closely wound portion. As a result, the possibility of
buckling and plastic deformation can be prevented. This results
in a reduction in the diameter of the coil spring 209. Thus,
the spring force can be reduced and the size of the weight can
also be reduced. Consequently, the movable electrode 205 and
accordingly, the free fall sensor 201 can be thinned.
-
Further, in the embodiment, the coil spring 209 is
connected via the circular dish-shaped joint 208 to the
conductive pin 204 when cantilevered so as to be disposed in the
form of a beam. In this case, it is desirable that the conductive
pin 204, coil spring 209 and weight 210 should be connected
linearly on a horizontal central axis. In particular, the coil
spring 209 is flexible and accordingly, it is not always easy
to align the coil spring 209 on a central axis. However, a gap
between the coil spring 209 and the container 202 is reduced as
the free fall sensor becomes thinner or smaller in size.
Accordingly, a high assembly accuracy and strict dimensional
control are required in order that a stable switching operation
may be achieved.
-
The joint 208 is effective in the point that it renders
the connecting work easy when the conductive pin 204 and coil
spring 209 are connected together although the joint is not an
essential component in the movable electrode 205. In particular,
when the assembly is slightly inclined relative to the central
axis in assembly of the movable electrode 205, the joint 208 is
held by tweezers and slightly flexed in the direction opposite
the inclination so that the assembly is corrected, whereby the
inclination is adjusted and corrected. Consequently, the coil
spring 209 and weight 210 or the movable electrode 205 can be
aligned along the proper axis. The joint is thus useful as an
assembly adjusting member.
-
Further, according to the embodiment, the weight 210 is
formed into the shape of an oblong circular column and connected
to the free end of the coil spring 209. Consequently, necessary
gravity can be ensured easily while the diameter of the weight
is reduced. Further, the thickness of the electrode structure
can also be reduced. Further, since the container 202 is also
formed into the cylindrical shape, it can be disposed in every
direction together with the movable electrode comprising the
coil spring 209, weight 210 and the like. Moreover, the joint
208, coil spring 209 and weight 210 are sequentially connected
to the conductive pin 204 so as to confront one another each in
the circular shape. As a result, these components can be
assembled easily without any directional limitation and the
aforementioned arrangement is effective in improving the
designing and manufacturing efficiencies.
-
The following effects can be achieved from the foregoing
embodiment. Since the container 202 serving as the fixed
electrode, the coil spring 209 and the weight 210 both serving
as the movable electrode 105 and the like are each formed into
a circular shape, the free fall sensor can readily be incorporated
into the equipment such as a portable computer without limitation
of a mounting angle. The free fall sensor thus produced can
detect the falling state of the equipment by a normal switching
operation, so that a quick countermeasure can be taken.
-
In particular, in order that the aforementioned
performance may be maintained for a long time, the embodiment
employs means for protecting the coil spring 209 against the shock
due to the falling or the like. In order that the coil spring
209 may be restrained from being forced to undergo via the weight
210 large flexure in the compressing direction. The
displacement limiting means is provided for limiting an amount
of displacement of the coil spring 209 within a predetermined
range. More specifically, the circularly cylindrical core
member 211 which protrudes integrally from the weight 210 side
is loosely inserted in the inner space of the coil spring 209.
The core member 211 has the length L1 shorter than the effective
length L0 of the coil spring 209 so as to allow necessary flexure
of the coil spring and limits large flexure (L0>L1).
-
Consequently, an excessive flexure of the coil spring 209
in the compressing direction is limited to an amount of
displacement corresponding to the predetermined dimension S when
the core member 211 is blocked by the joint 208 which is a member
at the conductive pin 204 side. Accordingly, the coil spring
209 can be used without buckling and plastic deformation and
predetermined quality and function can be maintained for along
period of time. Thus, the free fall sensor 201 having an eminent
durability can be provided. Further, since a large variation
in the weight 210 and particularly degree of collision against
the container 2 are reduced, sound due to collision or vibration
can also be restrained.
-
Thus, the free fall sensor 201 is superior in the original
functions and has the following eminent characteristics.
Firstly, since the weight 210 is oblong, a required weight can
be set and ensured even when the diameter of the weight is reduced.
Further, since the weight is connected in the direction of
elongation of the coil spring 209, the electrode structure can
be set at a minimum thickness and miniaturization suitable for
thin type of sensors can be achieved. Additionally, the movable
contact comprises the coil spring 209 and the oblong weight 210.
As a result, when the weight 210 collides against the container
202, the damping effect that the shock is received so as to be
damped can be expected, whereupon sound due to the collision of
the weight 210 against the container 202 can be reduced. With
this, the weight 210 can be maintained in the state where the
distal end thereof is in contact with the inner face of the
container 202 and the number of bound can be rendered minimum
and a bounding distance can be rendered small even if the weight
bounds. Consequently, noise due to the collision can
effectively be reduced.
-
Consequently, the chattering of the switching function due
to repeated contact and separation of the electrodes can be
reduced and accordingly, the possibility of malfunction
resulting from turn-off of the free fall sensor can be avoided,
for example. Additionally, there is a possibility that the sound
due to the collision of the weight 210 against the container 202
may become a noise when the portable computer is carried as well
as in the falling. Accordingly, the effect by the damping
improves the product value.
-
The damping effect is obtained from vertical expansion and
contraction of the coil spring 209, whereas the wiping effect
is obtained from the effective use of the lengthwise expansion
and contraction. More specifically, the weight 210 slides right
and left on the inner face of the container 202 while in contact
with the latter, whereby soil or oxide film on each contact face
is removed. This can provide a stable switching operation for
a long period of time and in particular, this can wipe out the
possibility of unstable operation due to reduction in the contact
pressure between the electrodes for miniaturization of the
sensor.
-
The core member 211 is formed integrally with the weight
210 in the embodiment. However, for example, the core member
as a discrete member may be welded or bonded, instead. Further,
the material for the core member should not be limited to the
metal but it may be made of plastics or rubber. The location
of the core member should not be limited to the weight 210 side.
Modified forms of the displacement limiting means (tenth and
eleventh embodiments) will be described with reference to FIGS
19 and 20 respectively. Identical or similar parts are labeled
by the same reference symbols as those in the ninth embodiment
and will not be described. Only the difference will be
described.
-
Firstly, the tenth embodiment will be described with
reference to FIG. 19 (corresponding to FIG. 17). In the free
fall sensor 201 of the tenth embodiment, the core member 215
serving as the displacement limiting means for the coil spring
209 is caused to protrude from the joint 208 which is a member
at the conductive pin 204 side and is loosely inserted in the
inner space of the coil spring-209. The core member 215 is welded
or bonded to the joint 208. The other construction of the free
fall sensor of the tenth embodiment is substantially the same
as that of the ninth embodiment.
-
In the above-described construction, when the free fall
sensor is subjected to shock due to the falling or the like, the
weight 210 moves while compressing the coil spring 209, being
blocked by the distal end of the core member 215. As a result,
since the coil spring 209 is protected without receiving
excessive pressure from the weight 210, the plastic deformation
with large flexure can be prevented. Accordingly, the same
effect as achieved from the ninth embodiment can also be achieved
from the tenth embodiment with the original functions of the free
fall sensor 201.
-
FIG. 20 illustrates an eleventh embodiment and corresponds
to FIG. 1. In the eleventh embodiment, the core members 216
protrude oppositely from the weight 210 and the joint 208
respectively. Accordingly, the core members 216 comprise first
and second cores 216a and 216b respectively. An addition L1
of the lengths a and b of the core members 216 is set to be slightly
shorter than the effective length L0 of the coil spring 209
(L0>a+b=L1) . The other construction of the free fall sensor of
the eleventh embodiment is substantially the same as that of the
ninth embodiment.
-
Consequently, the core member 216 having the length L1
shorter than the effective length L0 of the coil spring 209 is
constructed. As in the above-described tenth embodiment, the
second core 216b at the weight 210 side is blocked by the first
core 216a at the joint 208 side, whereby the displacement of the
coil spring 209 is limited in subjection to shock. Accordingly,
large flexure is prevented such that the coil spring can be
prevented from plastic deformation or the like.
-
FIGS. 21 to 23 illustrate twelfth to fourteenth embodiments
of the invention. These embodiments relate to the displacement
limiting means for the coil spring 209. Identical or similar
parts are labeled by the same reference symbols as those in the
ninth embodiment and will not be described. Only the difference
will be described.
-
FIG. 21 illustrates the twelfth embodiment and corresponds
to FIG. 1. In the twelfth embodiment, the displacement limiting
means blocks the movement of the weight 210 by making use of the
joint 217. More specifically, the joint 217 is formed into a
bottomed cylindrical shape. The joint 217 includes a
cylindrical portion 217a into which the coil spring 209 is loosely
inserted (large diameter).
-
The weight 210 has such a diameter as to be blocked by the
distal end of the cylindrical portion217a. The weight 210
confronts the cylindrical portion 217a with a predetermined
distance S defined therebetween when in the stationary or free
state. Accordingly, the coil spring 209 is covered by the joint
217 except for a part corresponding to the distance S. A
protrusion 210a protrudes integrally from a connected portion
of the coil spring 209 at the weight 210 side. The protrusion
210a serves as a joint effectively rendering the fitting of the
closely wound portion 209b easier and supporting the closely
wound portion in order that the coil spring 209 may easily be
connected by the bonding agent.
-
According to the above-described embodiment, since a
displacement amount of the coil spring 209 in the compression
direction is set at the predetermined distance S, the joint 217
and the weight 210 are moved by the distance S upon receipt of
shock due to the falling and thereafter, the weight 210 is blocked
by the joint 217, whereupon further flexure is prevented and
plastic deformation is avoided. Accordingly, since the coil
spring 209 can be protected against the plastic deformation for
a long period of time, the free fall sensor 201 with high
durability can be provided as in the foregoing embodiments.
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FIG. 22 illustrates a thirteenth embodiment of the
invention. In the thirteenth embodiment, the joint 208 and the
weight 218 confront each other with the distance S defined
therebetween as in the twelfth embodiment. Upon subjection to
shock, the weight 218 is blocked by the joint 208 such that the
coil spring 219 is prevented from displacement over the distance
S.
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The coil spring 219 has a smaller diameter in order to be
disposed inside the weight 218 as will be described later. The
closely wound portions 219a and 219b on both ends of the coil
spring 219 are connected to the joint 208 and the weight by the
bonding agent respectively.
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The joint 208 to which the closely wound portion 219a is
bonded is the same as used in the first embodiment. The weight
218 has a conical recess 218a formed in the end thereof to which
the closely wound portion 219b is bonded. A large part of the
coil spring 219 is enclosed in the recess 218a. Moreover, the
weight 218 has an outer diameter substantially equal to the outer
diameter of the joint 208. In short, the dish-shaped end of the
joint 208 confronts an outer peripheral end of the weight 218
at the recess 218a side and the distance S is defined therebetween
when in the stationary or free state. The coil spring 219 has
such a diameter as to be loosely inserted in the recess 218a (small
diameter).
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In the thirteenth embodiment, too, the joint 218 is
utilized as the means for limiting the displacement amount of
the coil spring 209 in the compression direction to the distance
S. Consequently, the thirteenth embodiment can achieve the same
effect as the twelfth embodiment. The recess 218a should not
be limited to the conical shape but may be cylindrical with a
larger inner diameter. In this case, the diameter of the coil
spring 219 is increased.
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FIG. 23 illustrates a fourteenth embodiment of the
invention and corresponds to FIG. 17. The movable contact 205
in the fourteenth embodiment has substantially the same
construction as that in the ninth embodiment. On the other hand,
the container 220 includes a reduced-diameter portion 220a which
is formed in the middle thereof so as to protrude inward. The
reduced-diameter portion 220 a has annnular constricted shape.
More specifically, the left end of the weight 210 is caused to
abut directly against the reduced-diameter portion 220a.
Further, the reduced-diameter portion 220a is located so as to
be spaced away from the left end of the weight 210 with the
predetermined distance S defined therebetween.
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According to the above-described construction, when the
weight 210 moves in the compression direction of the coil spring
209 upon subjection to shock due to the falling or the like, the
left end of the weight 210 abuts against the reduced-diameter
portion 220a such that further movement of the weight 210 is
blocked. More specifically, the coil spring 209 is allowed to
deform by compression by an amount corresponding to the distance
S but prevented from large flexure resulting in the plastic
deformation. Accordingly, the reduced-diameter portion 220a
limits the movement of the weight 210 and consequently serves
as displacement limiting means for limiting displacement of the
coil spring 209. Thus, the free fall sensor 201 with high
durability and stable performance can be provided. The
reduced-diameter portion 220a is provided for blocking the
weight 210 and accordingly should not be limited to the annular
continuous shape. The reduced-diameter portion may protrude
inward discontinuously or partially. In this case, too, the same
effect as described above can be achieved.
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Each of the container and the coil spring should not be
limited to the cylindrical shape. For example, when the core
member is not inserted in the inner space of the coil spring,
the coil spring may be conical or have the shape of a hand drum.
Furthermore, when the weight is directly blocked, a partial
protrusion corresponding to the large diameter portion may be
formed.